The old-fashioned turn-signal system, which has been the standard for about 100 years, is inconvenient to use, and therefore not used regularly by all drivers.
The traditional turn-signal control keeps you continually involved at a time when your attention should be 100% on your driving. Click your turn-signal on, and you have to remember to turn it off. Your standard turn-signal will sometimes turn itself off after completion of your turn, but not always. In the case of a lane-change, for example, your return to going straight may not be abrupt enough, and your turn-signal will continue to blink until you manually turn it off, perhaps several kilometers down the road.
The other option you have with the traditional turn-signal system is to keep the perfect pressure on the turn-signal lever until you are done signaling your turn or lane-change, and then release the lever. This action interferes with the ability of a driver to control the steering wheel. It also occupies the driver both physically and mentally at a time when the driver's total attention to driving is absolutely crucial.
Why do we use the turn-signal? The purpose of using your turn-signal is to eliminate surprises by informing others around you in advance what you plan to do. By making your turn-signal easier to operate, the turn-signal will be used regularly by most drivers, perhaps all. Traffic safety will improve, accidents will be reduced and so will injuries and fatalities.